Method of enhancing methane storage capacity in salt caverns

ABSTRACT

The present disclosure is directed toward a method for storing methane. The method for storing methane comprises several steps. A dissolving fluid comprising water is injected into a salt formation to produce a brine and a salt cavern within the salt formation. The brine is then removed from the salt cavern. A sorbent is then placed within the salt cavern before methane is injected into the salt cavern.

BACKGROUND

It is demonstrated that methane can provide clean and efficient energyfor power generation and other application including automobile andseveral other industrial uses. The worldwide production and consumptionof natural gas (methane, CH₄) has increased in recent years in a searchfor low carbon emission energy sources to tackle global warming.

Methane is utilized in various applications such as in automobile andseveral other industrial uses. In order to be used in theseapplications, methane must be stored through various means. Theconsumption of methane fluctuates with respect to utilization ofelectric power throughout the year. The limitation on methane or naturalgas storage facilities restricts the quantity of methane which has to bereserved for emergency and high-consumption periods.

Storage of methane underground, such as in salt caverns, may be usefulin the storage of energy for maintaining the stability of the naturalgas market and meeting the requirement of peak shaving.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

In one aspect, embodiments disclosed herein relate to a system and amethod for storing methane. The system for storing methane comprises asalt formation, an overburden, an underburden, a salt cavern within thesalt formation, a sorbent within the salt cavern, and a well traversingthe surface that connects the surface with the salt cavern. Theoverburden is proximal to the surface and adjacent to the saltformation, whereas the underburden is also adjacent to the saltformation but is distal to the overburden.

The method for storing methane comprises several steps. A dissolvingfluid comprising water is injected into a salt formation to produce abrine and a salt cavern within the salt formation. The brine is thenremoved from the salt cavern. A sorbent is then emplaced within the saltcavern before gas is injected into the salt cavern.

Other aspects and advantages of the claimed subject matter will beapparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustration of a methane storage system according toembodiments herein.

FIG. 2 illustrates a method 100 for effecting methane storage accordingto embodiments herein.

DETAILED DESCRIPTION

Methane has uses in applications that may range from the chemicalindustry, transportation fuel, and a means for storing energy. Methaneneeds to be stored in order to use it in one or more applications, suchas using it as an energy source or as an energy storage medium. Storageunderground in salt caverns can be used, but there is a limitation onthe availability of salt caverns around the world. Therefore, themodification of salt caverns to enhance the methane storage capacitycould lead to the efficient use of these geological structures.

Methane or natural gas may be stored, according to embodiments herein,in high surface area materials within engineered salt caverns toincrease the overall storage capacity in salt caverns. During orfollowing formation of an engineered salt cavern, sorbent materials maybe placed in the engineered salt caverns. Natural gas, when disposedwithin the sorbent-filled engineered salt cavern, will adsorb onto thesorbent materials, allowing for efficient subterranean gas storage. Thiswould enable energy storage to be carried out. In some embodiments, dueto the solid nature of sorbent, formation pressure in a salt formationthat is caused by weight of the overlying rock may be able to beresisted, at least in part, by the solid sorbent particles. This wouldreduce the needed amount of cushion gas, or the minimum pressure exertedby the gas, that fills a cavern to help maintain its shape, and thusincreasing the volume of working gas, in this case natural gas, that maybe withdrawn from the cavern. Here, “working gas” is defined as thevolume of gas that may be stored and withdrawn. The phrase “cushion gas”is defined as the minimum amount of gas that must remain in the saltcavern to help maintain its shape and prevent collapse, the cushion gasproviding a pressure force on the cavern walls.

In some embodiments, the role of “cushion gas” is filled by a minimumamount of gas that must remain in the salt cavern to help maintain itsshape and prevent collapse. In some embodiments, a greater mass of gasmay be stored than can be stored in an unfilled salt cavern alone, owingto the ability of some sorbents to store a greater mass of gas atpressure than an unfilled space and a reduced required amount of cushiongas. The maximum amount of working gas that may be stored in a saltcavern is bounded by the pressure from the rock above, the strength ofthe rock in the formation, and other properties. That is to say, themaximum total gas amount that may be stored in a salt cavern is definedby factors including the salt cavern's depth, the weight of the rockabove the salt cavern, the strength and resistance to fracture of thesurrounding rock, and other factors known to those skilled in the art,and, in embodiments herein, the added support provided to the cavern bythe solid sorbents disposed within the cavern for use in storing thegas.

There are several types of sorbents that may be used. “Sorbent” here isdefined as a material that supports physical storage of a gas thatconcentrates on the surface of the material. Typically, these materialshave large surface areas. In some embodiments, this allows gas to adsorbonto the surface, enabling a gas to be stored under pressure in asmaller space than would otherwise be possible. The higher adsorption ofgas of these materials originates from the adsorption of gases in themicroporous networks of these materials. Sorbents that are porous withmicroscopic pores of less than 2 nm in diameter are known here as“microporous materials”. Surface areas per gram of sorbents may varyfrom 100-7000 m²/g in some embodiments, from 500-5000 m²/g in otherembodiments, and from 1000-3000 m²/g in other embodiments. Pore volumeper gram of the sorbents may vary from 0.1-2.5 cm³/g in someembodiments. The pore volume per gram may be in a range with a maximumof any of about 2.5 cm³/g, 2.0 cm³/g, 1.5 cm³/g, 1.0 cm³/g, or 0.50cm³/g, and a minimum of any of about 0.1 cm³/g, 0.2 cm³/g, or 0.35cm³/g, with any maximum being capable of being combined with anyminimum. Micropore volume per gram of the sorbent may vary from 0.05-1.5cm³/g in some embodiments. Micropore volume per gram of the sorbent maybe in a range with a maximum of any of about 1.5 cm³/g, 0.75 cm³/g, or0.50 cm³/g and a minimum of any of about 0.05 cm³/g, 0.1 cm³/g, or 0.3cm³/g, with any maximum being capable of being combined with anyminimum. Sorbents may have a density that ranges from 0.1-2.5 g/cm³ insome embodiments, from 0.4-1.5 g/cm³ in other embodiments, and from0.5-1.0 g/cm³ in other embodiments.

In one or more embodiments, sorbents may have one or more shapes thatinclude, but are not limited to, spherical, cubic, oval, cylindricalpellets, capsules, fibers, or mixture of these. In one or moreembodiments, the sorbents may comprise materials that are organic,inorganic, organic-inorganic hybrids, or a mixture of these materials.The sorbents may also comprise materials that are amorphous,crystalline, polycrystalline or a mixture of these materials. In one ormore embodiments, activated carbons that may be generated from polymersor natural polymers may be used as sorbents. Sorbents may also comprisemetal-organic frameworks, amine-impregnated metal-organic frameworks. Inother embodiments, sorbents may comprise aluminosilicates orzeolite-type materials. In one or more embodiments, sorbents maycomprise porous silicates and porous silica. In one or more embodiments,sorbents may comprise porous polymers. Sorbents may also comprise acombination of two or more of these porous materials or other sorbentsas may be developed or known to those of skill in the art. In one ormore embodiments, sorbents may comprise microporous materials, whichallow enhanced storage and recovery of methane and other gases viapressure swing and are more suitable for systems that may cycle betweengas storage and gas consumption.

Sorbent particles may have a particle size that ranges from 5 to 1000microns in some embodiments, from 10 to 500 microns in otherembodiments, and from 50 to 100 microns in other embodiments.

Sorbent may be conglomerated into larger particles through the use ofbinders. These binders may be mixed with the sorbent to form largerconglomerations that may take the form of binder/sorbent particles, orparticles comprised of binder and sorbent. Average size of thebinder/sorbent particles may range from 1-20 mm in some embodiments. Inother embodiments, the size of the binder/sorbent particles may have arange with an upper limit of any of 20 mm, 10 mm, or 5 mm, and a lowerlimit of any of 1 mm, 2 mm, or 3 mm, with any upper limit being capableof being combined with any lower limit. The binder is characterized byits ability to form the sorbent into particles, and may comprise one ormore of bentonite, polymer, natural polymer, or other material capableof forming conglomerations. These conglomerations may also include othermaterials known to those skilled in the art for their ability to formconglomerations, to stabilize conglomerations, or for other purposes.

Methane molecules may diffuse easily through some geological formations.Salt formations are rock layers, the plurality of which is comprised ofa dissolvable salt material, such as sodium chloride or otherhalite-forming salts. Closer to the surface, above the salt formation,lies an overburden, which is the rock and/or soil that is adjacent toand rests on top of the salt formation. Below the salt formation is theunderburden, which is the rock and soil that is adjacent to and liesdirectly below the salt formation. The underburden is distal to theoverburden. The temperature of salt formations useful in embodimentsherein may range from 5-50° C., for example, from 10-35° C. in otherembodiments, and from 20-25° C. in other embodiments.

Salt caverns are man-made structures in salt formations. These saltformations have low permeability to the stored gas, such as, forexample, 10⁻⁶ to 10⁻⁹ millidarcy (mD), allowing for gas under pressureto remain in a cavern for long periods. Low permeability of saltformations facilitates the storage of gas within a salt cavern producedwithin them. In one or more embodiments, the permeability of theformation may be less than about 10⁻¹⁵ m². In one or more embodiments,the permeability of the formation may have a range with an upper limitof any one of 10⁻¹⁵ m², 10⁻¹⁸ m², or 10⁻²¹ m². In one or moreembodiments, the permeability of the formation may range from about10⁻¹⁵ m² to less than 10⁻²¹ m². This allows for storage of gas, as saltcaverns are typically made to have volumes ranging from about 100,000 m³to about 5,000,000 m³. The volume range may have an upper limit of anyof 5,000,000 m³, 3,000,000 m³, or 1,000,000 m³, and a lower limit of anyof 100,00 m³, 200,000 m³, or 500,000 m³, with any upper limit beingcombinable with any lower limit. Larger or smaller volumes are possiblein some embodiments.

In some embodiments, the salt cavern may be formed having a shape suchas cylindrical, ellipsoid, or capsule-shaped. In other embodiments, suchas salt caverns in bedded salt formations, the cavern may have anirregular geometry. The salt cavern may have a diameter, or effectivediameter, ranging from 5 m to 100 m in some embodiments, from 10 m to 50m in other embodiments, or from 25 m to 40 m in other embodiments. Thelength of the salt cavern may range from 100 m to 2000 m in someembodiments, from 200 m to 1000 m in other embodiments, or from 300 m to500 m in other embodiments. The sizes of salt caverns that can beproduced may depend on the initial size of the salt formation, theamount of methane that is desired to be stored, along with the stabilityof the salt cavern, or its ability to remain structurally intact overlong periods. This size, the strength of the walls of the cavern, andits depth from the surface are some parameters that need to beconsidered in the design of salt caverns and multiple salt cavernsystems.

In some embodiments, a salt cavern may be created by drilling a wellinto a salt formation and injecting a dissolving fluid into the saltformation that facilitates dissolution of the salt. This dissolvingfluid is typically water, in the form of fresh water, sea water, orbrine-based aqueous fluids, but may comprise other compounds ormaterials. A cavern that is formed by this process is filled with brine(dissolving fluid comprising dissolved salts). The solvation of salt maybe carried out at various leaching rates 0.1-30 m³/h, which may dependon the temperature. The brine is subsequently removed, leaving behind asalt cavern of a particular size or dimension. Insoluble material in thesalt formation may fall to or accumulate at the bottom of the cavern.

Injection of the dissolving fluid and removal of the brine may beperformed using a single pipe or multiple pipes. For example, multiplepipes may be disposed through the same well in some embodiments, with asmaller diameter pipe inside of a larger diameter pipe, leaving an openannulus in the larger diameter pipe and an open channel in the smallerdiameter pipe. In one or more embodiments, the smaller diameter pipe maybe longer, with dissolving fluid being injected into the formationeither via the shorter or longer pipe. The dissolving fluid may beinjected via the larger pipe, through the annulus, and withdrawn throughthe inner pipe, in some embodiments. In other embodiments, thedissolving fluid may be injected via the inner pipe and withdrawnthrough the annulus. The annular pipe may terminate, for example,proximate a roof of the cavern, while the inner pipe may be extendedduring cavern formation to be proximate a bottom of the cavernthroughout the cavern-forming process. The circulation pattern andinjection method, among other variables, may influence cavern shape andsize.

Dissolving fluid may be injected into the formation multiple times toproduce a salt cavern of desired dimensions. Compressed gas, such asair, may be used to remove the dissolving fluid, to remove contaminants,and to prevent collapse of the salt cavern during formation (thecompressed gas providing a cushion gas during cavern formation). Thebrine and insoluble particles may be removed with compressed air at apressure that may range from 15-3000 psi. Typical depths of the roof ofthe salt cavern from the surface may range from 100 m to 5000 m in someembodiments, from 500 m to 2500 m in other embodiments, and from 1000 mto 1500 m in other embodiments. In some embodiments, salt caverns ofother dimensions or those produced through other methods may be possibleas well. In one or more embodiments, a field of multiple salt caverns ina salt formation may be employed. In one or more embodiments, more thanone well may be drilled for a single salt cavern, particularly in thecase of salt formations that are more than 500 m thick or in othersituations apparent to those skilled in the art. The number of wells maybe governed, for example, by the size and shape of the salt layers.

After a salt cavern is produced, sorbents suitable for adsorbing the gasto be stored are then placed in the cavern. In some embodiments, thesorbent may be placed by a carrying fluid, characterized by its abilityto carry the sorbent into the salt cavern. The carrying fluid may be aliquid, a gas, or other material suitable for carrying the sorbent. Insome embodiments, the carrying fluid is a liquid, and the sorbent iscarried into the salt cavern as a dispersion or slurry in the liquid.The concentration of sorbents in the carrying fluid may vary from 1-75wt %. In one or more embodiments, placing the sorbents in the saltcavern is done in several steps, where the sorbent in the carrying fluidis pumped into the salt cavern, the sorbents are allowed to settlegravitationally, and the excess carrying fluid is then removed from thesalt cavern through compressed air pressurization. The time required tosettle the sorbent varies with respect to sorbent density and may rangefrom 1 hour to 24 hours. The compressed gas may also be used as acushion gas during sorbent injection to prevent wall collapse. Injectionof sorbent with concurrent removal of liquids or other carrier fluids isalso envisioned.

In one or more embodiments, vacuum or pressure is employed to facilitateremoval of the carrying fluid once the salt cavern has been filled withsorbents, leaving behind a salt cavern filled with dry sorbent. In oneor more embodiments, the range of sorbent quantity may have an upperlimit of any of about 2 million metric tons, 1 million metric tons, or0.5 million metric tons, and a lower limit of any of 50 metric tons, 500metric tons, or 1000 metric tons, with any upper limit being combinablewith any lower limit.

In some embodiments, for example, following cavern formation, the outerpipe may be proximate a cavern roof, and the inner pipe may be proximatea floor of the cavern. A slurry of sorbents may be injected via theannulus, and the liquids may be withdrawn through the inner pipe. Toprevent undesired entrainment of sorbent with the removed liquids, afilter or other device restricting influx of sorbent to the inner pipemay be used in some embodiments. In other embodiments, filtration maynot be used. In one or more embodiments, the sorbent may be in the formof pellets or monoliths held together using binders, rather than in afine powdered form and filtration may not be part of the operation. Inthese cases, the density and size of the sorbents/binder particles isgreat enough that the particles may settle in the cavern based on theirdensities, allowing separation of particles from carrying fluid viasedimentation.

As noted above, sorbent may be disposed into the cavern and allowed tosettle via gravity. Natural settling of the sorbents, however, mayresult in an inefficient filling of the cavern with sorbent, especiallyfor sorbents that do not easily flow. Free-flowing sorbents may fill thecavern more readily, but even free-flowing sorbents may have difficultyin completely filling the top of the cavern. Agitation or dispersiondevices may be used to ensure that the cavern is properly filled and/orto promote settling of the sorbents. In one or more embodiments,downhole tools may be used through the drill pipe to place the sorbentand fluid into the cavern. For example, among other tools that may beused, various tools that may provide for control of the direction offlow into the cavern may be used to facilitate distribution. The saltcavern may be filled step-by-step to improve filling characteristics.

As one skilled in the art could readily envisage, filling a cavern witha sorbent may result in an uneven distribution of the sorbent within thecavern. Efficient distribution and settling (packing) of the sorbentwithin the volume of the cavern may provide for the maximum supportbeing provided by the sorbent to the walls of the cavern, thusmaximizing the working volume (minimizing the needed cushion gas volumeor pressure) and minimizing the possibility for collapse or other damageto the cavern.

In some embodiments, placement of the sorbent according to embodimentsherein may result in the sorbent occupying at least 90 vol % of thecavern (total volume of solids, including void space between particles),at least 95 vol % of the cavern in other embodiments, and at least 98vol % or at least 99 vol % of the cavern in other embodiments. In yetother embodiments, 100 vol % of the cavern may be occupied by sorbent,and in yet other embodiments, the cavern may be over-filled with sorbentsuch that a portion of the well, below any valving or other sealingdevice attached to the well, also includes a volume of sorbent. Theover-filling of the cavern may ensure each of the walls (floor, sides,and ceiling) are supported by sorbent, as well as providing some volumeof sorbent to account for any additional settling of the sorbent thatmay occur due to pressurization and depressurization during normal useof the cavern. In one or more embodiments, it is preferred to fill thesalt cavern as much as possible because the sorbent provides cavernstability in addition to enhanced storage capacity. Minimizing the headspace unfilled with sorbent will provide maximum wall support and amaximum working volume. Accordingly, embodiments herein may provide forcontact of a portion of the sorbent with each wall of the cavern(bottom, sides, and top), thereby providing support to each wall of thecavern.

Methane gas is then inserted into the sorbent-filled salt cavern. Themaximum amount of compressed methane that may be inserted into thesorbent-filled salt cavern is determined by the methane storage capacityof the sorbent, based on the pressure and temperature conditions of thesalt cavern. Once the desired amount of gas is inserted in thesorbent-filled salt cavern, the well head of the sorbent-filled saltcavern is sealed. Releasing pressure at the surface can allow for thedesorption of gas from the sorbent and the removal of gas from thesorbent-filled salt cavern. Methane may then be stored and released, asdesired, to provide gas to the various end uses as noted above. Themethane storage capacity may be increased up to 4-fold in a cavernfilled with sorbent when compared with an empty cavern. The pressure ofthe methane after sealing may be in a range of about 500 psig to about3000 psig.

FIG. 1 is an illustration of a methane storage system according toembodiments herein. In FIG. 1 , a well 1 traverses an overburden 3 andenters a salt formation 5, forming a pathway to a salt cavern 7.Underneath the salt formation 5 is an underburden 9. Inside of the saltcavern 7 is a methane-adsorbed sorbent 11, and methane gas 13 is storedin the cavern, both absorbed onto the sorbent and in the free spacewithin the cavern. The well head is sealed, such as by a valve or otherappropriate device, to prevent escape of the methane when not beingextracted.

FIG. 2 illustrates a method 100 for effecting methane storage accordingto embodiments herein. Method 100 is representative of some embodimentsof a method for producing a sorbent-filled salt cavern and storingmethane. In method 100, a well 1 is drilled through an overburden 3 intoa salt formation 5, traversing the overburden 3 and entering the saltformation 5. The salt formation lies atop an underburden 9. A dissolvingfluid, such as water or other solvents with sufficient salt dissolutioncapability and carrying capacity, is injected (step 21) into the saltformation 5 through the well 1. The dissolving fluid dissolves part ofthe salt formation 5. A salt cavern is created by the process ofsolution mining, where a feed solvent is injected (step 21) into awellbore drilled into a subsurface salt formation. The brine thusgenerated by dissolving (leaching) the formation salt is then extracted(step 23) to create the cavity in the subsurface. The process ofdissolution and brine extraction are repeated over multiple cycles untila cavern of desired dimensions in created in the subsurface.

The generally preferred shape for salt caverns is a generallycylindrical cavity several hundred meters high and 50-80 meters (m) indiameter. Depending upon the formation being dissolved and the desiredshape of the cavern, direct (inject solvent at bottom of cavern,withdraw brine from top) or reverse (inject solvent at top, withdrawbrine from bottom of cavern) brine circulation may be used to create thecavern. While the circulating solvent/brine may provide some weight(pressure) to support the cavern walls, a cushion gas, such ascompressed air or compressed nitrogen, may be provided during the cavernformation process to ensure that the cavern is fully supported as it isbeing created.

The brine is then removed (step 23), leaving behind insolubles 15 and asalt cavern 7. The dehydration of the salt cavern can be carried out toremove water or brine from the caverns. The compressed air can be usedfor removing contaminates from the salt caverns and the cavern may bepressured with compressed air during the dehydration step to restrictthe salt caverns from collapsing due to formation pressure.

Following formation of the salt cavern 7, sorbent—carrier fluid mixture17 may be disposed within the cavern (step 25). In some embodiments, aslurry, comprising a carrying liquid and a sorbent, is injected (step25) into the salt cavern 7. The slurry of sorbent 17 (dispersed inliquid—aqueous or nonaqueous) is pumped (step 25) into the salt cavern 7in several steps. During each step, the sorbent 17 will be allowed tosettle down gravitationally and the excess liquid is evacuated usingcompressed air. In other embodiments, the solid sorbents may be flowed(step 25) into the salt cavern 7 without the aid of a liquid, ortransport of the solid sorbents may be facilitated using a carrier gas,such as air or nitrogen.

Once the salt cavern 7 is filled with the sorbent-carrier fluid mixture17, the liquid can be removed through vacuum or pressure (step 27). Inthese embodiments, compressed gas 18 is injected, causing the carryingliquid to be removed (step 27), leaving behind a salt cavern filled withsorbent 19 and compressed gas 18. The pressure of the compressed gasmay, for example, push the liquids out of a pipe extending to a floor ofthe cavern; a “dry” gas may also be used to remove liquids, such aswater or other carrier fluids, from the sorbent. A dry gas is a lowhumidity gas that is capable of the uptake of water or moisture.

Methane gas 13 is then pumped (step 29) into the salt cavern 7 filledwith sorbent 17. Methane gas 13 is compressed in the sorbent-filled saltcavern according to the theoretical capacity of the sorbents 17 based onthe pressure and temperature condition of the salt cavern. Methane gas13 adsorbs onto the sorbents 17, producing methane-adsorbed sorbent 11.On reaching the maximum methane storage capacity, the well head of thesalt caverns is closed (step 31) for long-term methane storage. In oneor more embodiments, closing the well head of the salt caverns (step 31)may be done via closing a valve on the surface. The methane gas 13 fromthe methane-adsorbed sorbent 11 can be released according to requirementfrom the surface through pressure release valves.

Other embodiments of the present invention aside from method 100 may bepossible, using differing configurations, materials, and method stepsreadily envisioned by those skilled in the art based on the presentdescription.

Example 1

In Example 1, theoretical storage capacity of salt caverns with a totalvolume of 1,005,459 m³ at different pressures are shown at 25° C.Methane storage capacity without sorbent (open volume) is calculatedusing the ideal gas law. To derive the CH₄ storage capacity, the CH₄storage capacity measured at 25° C. at different pressures wascalculated using carbon-based materials. The adsorbent material employedto fill the salt cavern is activated carbon monolith which has a densityof 1.07 g/cm³, a surface area of 1050 m²/g, and a pore volume of 0.87cm³/g, and is supplied by ATMI/Entegris Inc. Sorbent data obtained fromMarco-Lozar et al. (Carbon, 76, 123, 2014) and Prosniewski et al.(Adsorption, 24, 541, 2018).

Storage capacity with sorbent is calculated based on the amount of CH₄adsorbed on the basis of the mass of adsorbent that is needed to fillthe volume of the empty cavern. The different pressures representdifferent salt cavern depths. Methane storage capacity varies withrespect to depth (formation pressure). Theoretical storage capacitiesare shown below in Table 1.

TABLE 1 CH₄ storage capacity of empty salt cavern and adsorbent-filledsalt cavern. CH₄ storage capacity, KT (KiloTon) Pressure Empty SaltAdsorbent filled (psig) Caverns Salt Caverns 500 25 111 (4.4 times) 100040 136 (3.4 times) 1500 75 161 (2.1 times) 2000 111 171 (1.5 times) 3000161 181 (1.12 times)

As described above, embodiments herein provide for forming a saltcavern, disposing a sorbent within the salt cavern, and storing gas inthe sorbent-filled salt cavern. Use of a sorbent within the cavernadvantageously provides a larger working gas volume (minimum amount ofgas pressure required to prevent wall collapse) than for a cavern alone.Embodiments herein thus provide a method and system for the efficientstorage of large volumes of gas, which may be repeatedly withdrawn andreplenished, for use in various energy conversion or chemical conversionprocesses.

Although only a few example embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications are possible in the example embodiments without materiallydeparting from this invention. Accordingly, all such modifications areintended to be included within the scope of this disclosure as definedin the following claims.

What is claimed:
 1. A method for storing methane comprising: injecting adissolving fluid comprising water into a salt formation, producing asalt cavern within the salt formation and a brine; removing the brinefrom the salt cavern; placing a sorbent within the salt cavern; andinserting methane into the salt cavern.
 2. The method of claim 1,wherein placing the sorbent within the salt cavern comprises injectinginto the salt cavern a slurry comprising a carrying liquid and thesorbent.
 3. The method of claim 2, wherein the placing further comprisesallowing the sorbent to settle within the salt cavern, removing at leasta portion of the carrying liquid from the salt cavern, and injecting anadditional volume of the slurry into the salt cavern.
 4. The method ofclaim 3, wherein the injecting, allowing to settle, and the removing arerepeated until at least 95 vol % of the salt cavern is filled with thesorbent.
 5. The method of claim 1, wherein placing the sorbent withinthe salt cavern comprises transporting the sorbent into the salt cavernusing a compressed gas.
 6. The method of claim 5, wherein the compressedgas is air.
 7. The method of claim 1, wherein placing the sorbent withinthe salt cavern comprises at least one of distributing the sorbentwithin the salt cavern and agitating the sorbent within the salt cavernto facilitate settling of the sorbent.
 8. The method of claim 1, whereinthe sorbent comprises at least one microporous material selected fromthe group consisting of: activated carbons, metal organic frameworks,porous polymers, aluminosilicates, zeolites, porous silicates, andporous silica.
 9. The method of claim 8, wherein the sorbent comprisesthe at least one microporous material and a binder.
 10. The method ofclaim 1, further comprising sealing the well head of the salt cavernafter the inserting.
 11. The method of claim 10, wherein the pressure ofthe methane after the sealing is in a range from 500 psig to 3000 psig.